Bao-cao-al{11 o{11 {11 glass compositions

ABSTRACT

Glasses in the BaO-CaO-Al2O3 composition system useful in the manufacture of refractory glass fibers and wools for insulation and metal casting applications wherein silica-containing wools and fibers pose a health hazard are described.

[4 1 Dec. 3, 1974 1 BAO-CAO-AL O GLASS COMPOSITIONS [75] Inventor:Robert F. Davis, Cary, NC.

[73] Assignee: Corning Glass Works, Corning,

[22] Filed: Oct. 20, 1972 [2]] Appl. No.: 299,628

52 Us. Cl. 106/50, 106/47 R [51] Int. Cl. (03c 13/00 [58] Field ofSearch 106/50, 47 R, 47 Q [56] References Cited UNITED STATES PATENTS3,007,804 11/1961 Kreidl 106/47 X 3,545,639 12/1970 Charles 106/47 X3,635,739 1/1972 MacDowell 106/47 X 3,687,850 8/1972 Gagin 106/50X OTHERPUBLICATIONS Florence, F. M., et 21].; Transmittance of Some CalciumAluminate and Germanate Glasses, Journ. of Research Natl. Bur. Stds. 55(1955) pp. 231-237.

Primary ExaminerWinston A. Douglas Assistant ExaminerJ0hn F. NieblingAttorney, Agent, or Firm-Kees van der Sterre; Clarence R. Patty, Jr.

[57] ABSTRACT 6 Claims, 2 Drawing Figures 11 BAO-CAO-AlL o GLASScowmosrrrous BACKGROUND OF THE INVENTION It is known that a smallglass-forming region exists in the BaO-CaO-AI O composition system. Forexample, F. M. Florence et al. in Infrared Transmittance of Some CalciumAluminate and Germanate Glasses, Journal of Research of the NationalBureau of Standards, Vol. 55, pp. 231-237 (1955), describe the infraredlight-transmitting properties of several compositions in this field. H.C. Hafner et al. in Optical and Physical Properties of Some CalciumAluminate Glasses. American Ceramic Society Journal, Vol. 41, pp.315-323 (1958) also report the melting of several such compositions,with and without additives such as alkali and alkaline earth metaloxides, and the resulting optical properties of these glasses.

The information obtained fron these and other prior art referencessuggest that the glass-forming region in the BaO-CaO-AI O compositionsystem is small and rather well defined, and that most known BaO-CaO- A1melts devitrify readily and are difficult to form without somecrystallization. Yet the refractory nature of BaO-caO-Al O glasses is animportant property which could be utilized in a variety ofhigh-temperature applications, provided good glass-forming compositionsand means for forming them into useful articles could be devised.

SUMMARY OFTHE INVENTION I have now discovered an area of BaO-CaO-AI Oglass composition useful in the production of glass fibers or wool forhigh-temperature applications. Notwithstanding the fact that thediscovered composition area is outside the region previously thought tobe useful for glass-making, the fibers are of good glassquality and haveexcellent refractory properties. Thus they are useful in hightemperature insulation and molten metal casting applications as asubstitute for injurious asbestos fibers or other silica-containingmaterials.

The newly discovered BaO-CaO-AI O composition area is shown in FIG. 1 ofthe DRAWING as the region bounded by the polygon ABCDEFGA in theBaO-CaO- A1 0 ternary compositions diagram. The compositions are shownin mole percent on the oxide basis. The bulk of the compositions lie inthe region of about 4-18 mole percent BaO, 42-54 mole percent CaO and32-42 mole percent A1 0 A minor connected composition area includescompositions consisting essentially, in mole percent on the oxide basis,of about 0-7% BaO, 54-61% CaO, and 39-42% A1 0 The describedcompositions may be melted according to conventional glass-workingpractice at temperatures in the range from about 1,600l,800C. and may beformed using fiberand wool-forming processes well known in the art. Theproduct of the manufacturing process is a fibrous glass of a compositionwithin the above-described composition region. The fibers are completelyamorphous; however, electron micrographs show phase separation in theunzinnealed state which occurs during the forming process. This phaseseparat'ion does not, however, appear to deleteriously affect thestrength or other useful properties of the fibrous glass.

The refractory and amorphous properties of the fibrous glass arerespectively demonstrated by differential thermal analysis and X-raydiffraction data. The

former technique shows crystallization-to occur only upon heating attemperatures in excess of about 900C. Also, the melting points of theproducts of crystallization are in the l,250-1,410C. range.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 of the DRAWING is a ternaryphase diagram of part of the BaO-CaO-Al O composition system wherein thepolygon ABCDEFGA defines the composition region of the presentinvention.

FIG. 2 of the DRAWING is an electron micrograph showing an untreatedfracture surface of a bulk glass article of a composition within thescope of the present invention wherein phase separation typical of suchcompositions is evident.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Table I below sets forth anumber of examples of glasses coming within the composition rangeshereinabove described. The compositions are given in mole percent on theoxide basis as calculated from the batch.

Batch materials for the above compositions may comprise any ingredients,whether oxides or other compounds, which upon melting to form a glasswill be converted to the specified oxides in the proper proportions. Theabove compositions were prepared by compounding batches consisting ofalumina, calcium carbonate and barium carbonate, tumble-mixing for 1hour to insure homogeneity in the batch, and melting in platinum orplatinum-rhodium crucibles for four hours at temperatures in the rangefrom about 1,700-1,800C.

The melts prepared as above described were formed into a fibrousglasswool product by pouring the molten glass through a high velocitynitrogen stream which physically separated the molten glass into fibers.The fibers were collected on a steel screen, with successive layersbeing added until a thick mass of fibers forming a glass wool wasobtained. In each case the glass fibers forming the wool were of goodquality, free from devitrification and strong enough to resist extensivebreakage through handling.

Glasses within the disclosed composition region were examined withelectron microscopy, X-ray diffraction, and differential thermalanalysis techniques for the purpose of investigating the microstructureand physical properties thereof. Electron micrograph studies of bulksamples indicate that considerable phase separation occurs during theforming process. FIG. 2 of the DRAW- ING is an electron micrograph ofthe untreated fracture surface of a inches X 5 inches X 3 4 inchunannealed glass patty of the composition of Example 1 of 5 Table Iabove. The white bar appearing in the micrograph represents a length ofone micron. The rough surface texture which is clearly apparent at thismagnification suggests considerable phase separation, although the exactcomposition of the separated phases has not been determined. This phaseseparation has also been observed in other compositions shown in TableI, and is believed to be a feature common to all of the compositionswithin the scope of the present invention.

Powders of the fibrous glasses appearing in Table I were also examinedusing differential thermal analysis (DTA) techniques to determine thetemperature at which crystal formation and subsequent crystaldissolution occur. The DTA data are shown in Table II below for thecomposition examples from Table I upon which measurements were taken.The crystallization temperatures shown are those temperatures at whichrapid formation of crystals commences within the powders as they areheated, and the melting temperatures shown are those temperatures atwhich melting of the crystals formed at crystallization temmperaturesoccurs. The crystals formed are believed to be of 3CaO.Al O and BaO.CaOcomposition.

TABLE II Crystallization Melting Advantages of the fibrous glass for useat high temperatures, in addition to the advantage of being silicafree,include flexibility and a higher devitrification or crystallizationtemperature than most prior art refractory fibers or wools. Further, forapplications where crystallized fibers or wools can be employed, thecrystalline phases of the compositions of the invention are expected todemonstrate significantly higher melting temperatures than other priorart glasses which have been crystallized.

The compositions of the present invention are generally higher inalumina than prior art compositions, as well as somewhat higher in bariaand somewhat lower in lime, yet their melting and viscositycharacteristics are quite well suited for conventional fiberandwoolforming processes. This is somewhat surprising in view of the factthat high-alumina compositions would be expected to demonstrateproperties of rapid devitrification and low viscosity at the liquidswhich would render them unsuitable for fiber-forming operations.

I claim:

1. A composition for a glass which is composed, in mole percent on theoxide basis, of BaO, CaO and A1 0 in proportions falling within the areaor along the boundaries of the polygon ABCDEFGA shown in the BaO-CaO-AlO ternary composition diagram comprising FIG. 1 of the DRAWING.

2. A composition according to claim 1 wherein 8210 is present in anamount ranging from 4 to 18 mole percent, CaO is present in an amountranging from 42 to 54 mole percent, and A1 0 is present in an amountranging from 32 to 42 mole percent.

3. A composition according to claim 1 wherein BaO is present in anamount ranging from O to 7 mole percent, CaO is present in an amountranging from 54 to 61 mole percent, and A1 0 is present in an amountranging from 39 to 42 mole percent. 7

4. A fibrous glass which is composed, in mole percent on the oxidebasis, of BaO, CaO and N 0 in proportions falling within the area oralong the boundaries of the polygon ABCDEFGA shown in the BaO-CaO A1 0ternary composition diagram comprising FIG. 1 of the DRAWING.

5. A fibrous glass according to claim 4 wherein BaO is present in anamount ranging from 4 to 18 mole percent, C210 is present in an amountranging from 42 to 54 mole percent, and A1 0,, is present in an amountranging from 32 to 42 mole percent.

6. A fibrous glass according to claim 4 wherein 8210 is present in anamount ranging from 0 to 7 mole percent, CaO is present in an amountranging from 54 'to 61 mole percent, and Al O is present in an amountranging from 39 to 42 mole percent.

* =l l l

1. A COMPOSITION FOR A GLASS WHICH IS COMPOSED, IN MOLE PERCENT ON THEOXIDE BASIS OF BAO, CAO AND AL2O3 IN PROPERTIONS FALLING WITHIN THE AREAOR ALONG THE BOUNDARIES OF THE
 2. A composition according to claim 1wherein BaO is present in an amount ranging from 4 to 18 mole percent,CaO is present in an amount ranging from 42 to 54 mole percent, and Al2O3 is present in an amount ranging from 32 to 42 mole percent.
 3. Acomposition according to claim 1 wherein BaO is present in an amountranging from 0 to 7 mole percent, CaO is present in an amount rangingfrom 54 to 61 mole percent, and Al2 O3 is present in an amount rangingfrom 39 to 42 mole percent.
 4. A fibrous glass which is composed, inmole percent on the oxide basis, of BaO, CaO and Al2O3 in proportionsfalling within the area or along the boundaries of the polygon ABCDEFGAshown in the BaO-CaO-Al2O3 ternary composition diagram comprising FIG. 1of the DRAWING.
 5. A fibrous glass according to claim 4 wherein BaO ispresent in an amount ranging from 4 to 18 mole percent, CaO is presentin an amount ranging from 42 to 54 mole percent, and Al2O3 is present inan amount ranging from 32 to 42 mole percent.
 6. A fibrous glassaccording to claim 4 wherein BaO is present in an amount ranging from 0to 7 mole percent, CaO is present in an amount ranging from 54 to 61mole percent, and Al2O3 is present in an amount ranging from 39 to 42mole percent.